1. Field of the Invention
The invention relates to decoding signals, and more particularly, to methods and apparatus for decoding teletext and/or closed caption data embedded within signals such as video signals.
2. Description of the Related Art
Although watching television has been the national pastime of the United States and other countries for many years, the computer revolution has begun to expand the usefulness of television beyond its traditional role. Technological developments in recent decades have led to the advent of closed caption television, which integrates a secondary signal into the main television signal. The closed caption data may be decoded and displayed separately on the display system, for example to provide subtitles to hearing-impaired viewers.
An even more recent development is the advent of teletext, which provides a method of broadcasting data by integrating it into the television signal. Like closed caption data, the teletext information is integrated into the television signal without disrupting the television image. As information technology like the Internet develops, teletext is likely to assume a greater role in information systems.
Decoder systems for extracting the teletext and closed caption information from the television signal have been developed and made publicly available. These decoder systems are typically hardware systems integrated into the television circuitry. As the television signal is received by the television, the decoder system continuously monitors the incoming signal for codes indicating that teletext or closed caption data follows. The decoder system then decodes the data "on the fly" and provides it to the user.
Although conventional decoder systems effectively decode and present the data, they suffer several drawbacks. On of the most obvious problems is the cost. The circuitry required to perform the processing in real time is typically dedicated solely to detecting and decoding the teletext and closed caption data. Designing and manufacturing such dedicated circuitry is typically costly. In addition, such systems suffer limited flexibility, as alterations to hardware designs are often costly and difficult to implement, especially after the decoder system has been installed. Further, such systems may be subject to interference that, while of limited effect on the television image, may significantly affect the detection and decoding of the data.